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Think of the world's most prolific killers, and you might come up with a list that includes sharks, lions and even humans.

But our smaller, feline friends may be higher up on the list than previously thought, says a report in the journal Nature Communications.

Domestic cats kill between 1.4 billion and 3.7 billion birds and up to 20 billion small rodents each year, according to researchers at the Migratory Bird Center of the Smithsonian Conservation Biology Institute.

The report, published Tuesday, found that cats -- particularly strays -- are "likely the single greatest source of anthropogenic mortality for U.S. birds and mammals."

Though they are cute and cuddly, felines are actually finely tuned killers that affect wildlife to such an extent that the researchers have called on authorities to come up with ways to lessen their environmental impact.

"To maintain the integrity of our ecosystems, we have to conserve the animals that play integral roles in those ecosystems," said Dr. George Fenwick, president of the American Bird Conservancy. "Every time we lose another bird species or suppress their population numbers, we're altering the very ecosystems that we depend on as humans. This issue clearly needs immediate conservation attention."

A study conducted by the International Union for Conservation of Nature Red List of Threatened Species found that free-ranging cats on islands have caused or contributed to 33 of the modern bird, mammal, and reptile extinctions recorded by the group, or 14% of the total.

A free-ranging domestic cat is defined as a cat allowed to leave home and roam freely around the property not under the watchful eyes of its owner. Cats, not unlike lions and tigers, use two hunting strategies. They will either stalk their prey or wait to ambush the prey when it gets close enough. Owners of free-ranging domestic cats likely have had to dispose of a dead animal that their pets proudly returned home.